TAD boundary deletion causes PITX2-related cardiac electrical and structural defects

While 3D chromatin organization in topologically associating domains (TADs) and loops mediating regulatory element-promoter interactions is crucial for tissue-specific gene regulation, the extent of their involvement in human Mendelian disease is largely unknown. Here, we identify 7 families presenting a new cardiac entity associated with a heterozygous deletion of 2 CTCF binding sites on 4q25, inducing TAD fusion and chromatin conformation remodeling. The CTCF binding sites are located in a gene desert at 1 Mb from the Paired-like homeodomain transcription factor 2 gene (PITX2). By introducing the ortholog of the human deletion in the mouse genome, we recapitulate the patient phenotype and characterize an opposite dysregulation of PITX2 expression in the sinoatrial node (ectopic activation) and ventricle (reduction), respectively. Chromatin conformation assay performed in human induced pluripotent stem cell-derived cardiomyocytes harboring the minimal deletion identified in family#1 reveals a conformation remodeling and fusion of TADs. We conclude that TAD remodeling mediated by deletion of CTCF binding sites causes a new autosomal dominant Mendelian cardiac disorder.

An international multicenter cohort study on implantable cardioverter-defibrillators for the treatment of symptomatic children with catecholaminergic polymorphic ventricular tachycardia

BACKGROUND

Catecholaminergic polymorphic ventricular tachycardia (CPVT) may cause sudden cardiac death (SCD) despite medical therapy. Therefore, implantable cardioverter-defibrillators (ICDs) are commonly advised. However, there are limited data on the outcomes of ICD use in children.

OBJECTIVE

The purpose of this study was to compare the risk of arrhythmic events in pediatric patients with CPVT with and without ICD.

METHODS

We compared the risk of SCD in patients with RYR2 (ryanodine receptor 2) variants and phenotype-positive symptomatic patients with CPVT with and without ICD who were younger than 19 years and had no history of sudden cardiac arrest at phenotype diagnosis. The primary outcome was SCD; secondary outcomes were composite end points of SCD, sudden cardiac arrest, or appropriate ICD shocks with or without arrhythmic syncope.

RESULTS

The study included 235 patients, 73 with ICD (31.1%) and 162 without ICD (68.9%). Over a median follow-up of 8.0 years (interquartile range 4.3-13.4 years), SCD occurred in 7 patients (3.0%), of whom 4 (57.1%) were noncompliant with medications and none had an ICD. Patients with ICD had a higher risk of both secondary composite outcomes (without syncope: hazard ratio 5.85; 95% confidence interval 3.40-10.09; P < .0001; with syncope: hazard ratio 2.55; 95% confidence interval 1.50-4.34; P = .0005). Thirty-one patients with ICD (42.5%) experienced appropriate shocks, 18 (24.7%) inappropriate shocks, and 21 (28.8%) device-related complications.

CONCLUSION

SCD events occurred only in the no ICD group and in those not on optimal medical therapy. Patients with ICD had a high risk of appropriate and inappropriate shocks, which may be reduced with appropriate device programming. Severe ICD complications were common, and risks vs benefits of ICDs need to be considered.

Cardiomyopathy with an LMNA Genetic Variant Affecting Three Consecutive Generations: A Case Series

We report the case of a family afflicted with cardiac laminopathy who showed atrial fibrillation (AF) and complete atrioventricular block across three generations. Implantable cardioverter defibrillators (ICDs) implantation, or cardiac resynchronization therapy (CRT) were delivered to the three patients (proband; 61 years old, proband's mother: 84 years old, and proband's daughter; 38 years old) to prevent sudden cardiac death or suppress heart failure progression. A novel frameshift mutation (LMNA Exon 9: c.1550dupA;p. N518Efs*34) was found in all three cases through genetic testing, and this mutation may potentially result in the relatively late appearance of a phenotype of left ventricular systolic dysfunction.

Clinical characterization of type 1 long QT syndrome caused by C-terminus Kv7.1 variants

BACKGROUND

Variants in the KCNQ1 gene, encoding the α-subunit of the slow component of delayed rectifier K+ channel Kv7.1, cause long QT syndrome (LQTS) type 1. The location of variants may be one of the factors in determining prognosis. However, detailed genotype-phenotype relationships associated with C-terminus variants remain unelucidated.

OBJECTIVE

We investigated the clinical characteristics and variant-specific arrhythmic risks in patients with LQTS carrying Kv7.1 C-terminus variants.

METHODS

The study comprises 202 consecutive patients with LQTS (98 probands and 104 family members) who carry a rare heterozygous variant in the Kv7.1 C-terminus. Their clinical characteristics and arrhythmic events were investigated.

RESULTS

We identified 36 unique C-terminus variants (25 missense and 11 non-missense). The p.R366W variant was identified in 8 families, and p.T587M was identified in 21 families in large numbers from northwestern Japan. As for the location of the variant, we found that the variants in highly conserved regions and nonhelical domains were associated with longer QTc intervals compared with the variants in other regions. Both p.R366W and p.T587M variants are located in the highly conserved and functionally pivotal regions close to helices A and D, which are associated with calmodulin binding and channel assembly (tetramerization), respectively. The probands carrying p.T587M and p.R366W variants had worse arrhythmia outcomes compared with those with other C-terminus variants. The haplotype analysis of p.T587M families was suggestive of a founder effect.

CONCLUSION

The arrhythmic risk of C-terminus variants in Kv7.1 in LQTS is not homogeneous, and locations of variants can be a determining factor for prognosis.

Prognostic Value of Multiplexed Assays of Variant Effect and Automated Patch-clamping for KCNH2-LQTS Risk Stratification

Background

Long QT syndrome (LQTS) is a lethal arrhythmia condition, frequently caused by rare loss-of-function variants in the cardiac potassium channel encoded by KCNH2. Variant-based risk stratification is complicated by heterogenous clinical data, incomplete penetrance, and low-throughput functional data.

Objective

To test the utility of variant-specific features, including high-throughput functional data, to predict cardiac events among KCNH2 variant heterozygotes.

Methods

We quantified cell-surface trafficking of 18,323 variants in KCNH2 and recorded potassium current densities for 506 KCNH2 variants. Next, we deeply phenotyped 1150 KCNH2 missense variant patients, including ECG features, cardiac event history (528 total cardiac events), and mortality. We then assessed variant functional, in silico, structural, and LQTS penetrance data to stratify event-free survival for cardiac events in the study cohort.

Results

Variant-specific current density (HR 0.28 [0.13-0.60]) and estimates of LQTS penetrance incorporating MAVE data (HR 3.16 [1.59-6.27]) were independently predictive of severe cardiac events when controlling for patient-specific features. Risk prediction models incorporating these data significantly improved prediction of 20 year cardiac events (AUC 0.79 [0.75-0.82]) over patient-only covariates (QTc and sex) (AUC 0.73 [0.70-0.77]).

Conclusion

We show that high-throughput functional data, and other variant-specific features, meaningfully contribute to both diagnosis and prognosis of a clinically actionable monogenic disease.

Assessment of maxillary sinus fluid volume for postmortem diagnosis of drowning

INTRODUCTION

Drowning is a comprehensive and exclusive diagnosis at autopsy. Autopsy findings such as pleural effusion and waterlogged lungs contribute to the diagnosis. Herein, we aim to reveal the practical usefulness and postmortem changes of the maxillary sinus fluid volume to diagnose drowning.

METHODS

We evaluated 52 drowning and 59 nondrowning cases. The maxillary sinus fluid volume was measured using a computed tomography (CT) scan, and pleural effusion volume and lung weight were manually measured at autopsy. The utility of these three indices for diagnosing drowning and its postmortem changes was evaluated.

RESULTS

The maxillary sinus fluid volume was significantly higher in drowning cases than in other external causes and cardiovascular death cases. Receiver operating characteristic curve analysis revealed that a total maxillary sinus fluid volume >1.04 mL more usefully indicated drowning (odds ratio, 8.19) than a total pleural effusion volume >175 mL (odds ratio, 7.23) and a total lung weight >829 g (odds ratio, 2.29). The combination of maxillary sinus fluid volume and pleural effusion volume more effectively predicted drowning than one index alone. Moreover, the maxillary sinus fluid volume was less influenced by the postmortem interval than the other two indices up to a week after death.

CONCLUSION

Maxillary sinus fluid volume can be more useful than pleural effusion volume and lung weight with higher sensitivity and odds ratio for diagnosing drowning.

IMPLICATIONS FOR PRACTICE

Fluid accumulation in both the maxillary sinuses strongly predicts drowning in the postmortem imaging.

Flecainide Is Associated With a Lower Incidence of Arrhythmic Events in a Large Cohort of Patients With Catecholaminergic Polymorphic Ventricular Tachycardia

BACKGROUND

In severely affected patients with catecholaminergic polymorphic ventricular tachycardia, beta-blockers are often insufficiently protective. The purpose of this study was to evaluate whether flecainide is associated with a lower incidence of arrhythmic events (AEs) when added to beta-blockers in a large cohort of patients with catecholaminergic polymorphic ventricular tachycardia.

METHODS

From 2 international registries, this multicenter case cross-over study included patients with a clinical or genetic diagnosis of catecholaminergic polymorphic ventricular tachycardia in whom flecainide was added to beta-blocker therapy. The study period was defined as the period in which background therapy (ie, beta-blocker type [beta1-selective or nonselective]), left cardiac sympathetic denervation, and implantable cardioverter defibrillator treatment status, remained unchanged within individual patients and was divided into pre-flecainide and on-flecainide periods. The primary end point was AEs, defined as sudden cardiac death, sudden cardiac arrest, appropriate implantable cardioverter defibrillator shock, and arrhythmic syncope. The association of flecainide with AE rates was assessed using a generalized linear mixed model assuming negative binomial distribution and random effects for patients.

RESULTS

A total of 247 patients (123 [50%] females; median age at start of flecainide, 18 years [interquartile range, 14-29]; median flecainide dose, 2.2 mg/kg per day [interquartile range, 1.7-3.1]) were included. At baseline, all patients used a beta-blocker, 70 (28%) had an implantable cardioverter defibrillator, and 21 (9%) had a left cardiac sympathetic denervation. During a median pre-flecainide follow-up of 2.1 years (interquartile range, 0.4-7.2), 41 patients (17%) experienced 58 AEs (annual event rate, 5.6%). During a median on-flecainide follow-up of 2.9 years (interquartile range, 1.0-6.0), 23 patients (9%) experienced 38 AEs (annual event rate, 4.0%). There were significantly fewer AEs after initiation of flecainide (incidence rate ratio, 0.55 [95% CI, 0.38-0.83]; P=0.007). Among patients who were symptomatic before diagnosis or during the pre-flecainide period (n=167), flecainide was associated with significantly fewer AEs (incidence rate ratio, 0.49 [95% CI, 0.31-0.77]; P=0.002). Among patients with ≥1 AE on beta-blocker therapy (n=41), adding flecainide was also associated with significantly fewer AEs (incidence rate ratio, 0.25 [95% CI, 0.14-0.45]; P<0.001).

CONCLUSIONS

For patients with catecholaminergic polymorphic ventricular tachycardia, adding flecainide to beta-blocker therapy was associated with a lower incidence of AEs in the overall cohort, in symptomatic patients, and particularly in patients with breakthrough AEs while on beta-blocker therapy.

Holter Electrocardiographic Approach to Predicting Outcomes of Pediatric Patients With Long QT Syndrome

BACKGROUND

This study was performed to clarify the clinical findings of pediatric patients diagnosed with long QT syndrome (LQTS) through electrocardiographic screening programs and to predict their outcome using Holter electrocardiographic approaches.Methods and Results: This retrospective study included pediatric patients with a Schwartz score of ≥3.5 who visited the National Hospital Organization Kagoshima Medical Center between April 2005 and March 2019. Resting 12-lead and Holter electrocardiograms were recorded at every visit. The maximum resting QTc and maximum Holter QTc values among all recordings were used for statistical analyses. To test the prognostic value of QTc for the appearance of cardiac events after the first hospital visit, receiver operating characteristic curves were used to calculate the area under the curve (AUC). Among 207 patients, 181 (87%) were diagnosed through screening programs. The prevalence of cardiac events after the first hospital visit was 4% (8/207). Among QTc at diagnosis, maximum resting QTc, and maximum Holter QTc, only maximum Holter QTc value was a predictor (P=0.02) of cardiac events after the hospital visit in multivariate regression analysis. The AUC of the maximum Holter QTc was significantly superior to that of maximum resting QTc.

CONCLUSIONS

The maximum Holter QTc value can be used to predict the appearance of symptoms in pediatric patients with LQTS.

Calmodulinopathy in Japanese Children - Their Cardiac Phenotypes Are Severe and Show Early Onset in Fetal Life and Infancy

BACKGROUND

Cardiac calmodulinopathy, characterized by a life-threatening arrhythmia and sudden death in the young, is extremely rare and caused by genes encoding calmodulin, namely calmodulin 1 (CALM1), CALM2, and CALM3.Methods and Results: We screened 195 symptomatic children (age 0-12 years) who were suspected of inherited arrhythmias for 48 candidate genes, using a next-generation sequencer. Ten probands were identified as carrying variants in any of CALM1-3 (5%; median age 5 years), who were initially diagnosed with long QT syndrome (LQTS; n=5), catecholaminergic polymorphic ventricular tachycardia (CPVT; n=3), and overlap syndrome (n=2). Two probands harbored a CALM1 variant and 8 probands harbored 6 CALM2 variants. There were 4 clinical phenotypes: (1) documented lethal arrhythmic events (LAEs): 4 carriers of N98S in CALM1 or CALM2; (2) suspected LAEs: CALM2 p.D96G and D132G carriers experienced syncope and transient cardiopulmonary arrest under emotional stimulation; (3) critical cardiac complication: CALM2 p.D96V and p.E141K carriers showed severe cardiac dysfunction with QTc prolongation; and (4) neurological and developmental disorders: 2 carriers of CALM2 p.E46K showed cardiac phenotypes of CPVT. Beta-blocker therapy was effective in all cases except cardiac dysfunction, especially in combination with flecainide (CPVT-like phenotype) and mexiletine (LQTS-like).

CONCLUSIONS

Calmodulinopathy patients presented severe cardiac features, and their onset of LAEs was earlier in life, requiring diagnosis and treatment at the earliest age possible.

Clinical presentation of calmodulin mutations: the International Calmodulinopathy Registry

AIMS

Calmodulinopathy due to mutations in any of the three CALM genes (CALM1-3) causes life-threatening arrhythmia syndromes, especially in young individuals. The International Calmodulinopathy Registry (ICalmR) aims to define and link the increasing complexity of the clinical presentation to the underlying molecular mechanisms.

METHODS AND RESULTS

The ICalmR is an international, collaborative, observational study, assembling and analysing clinical and genetic data on CALM-positive patients. The ICalmR has enrolled 140 subjects (median age 10.8 years [interquartile range 5-19]), 97 index cases and 43 family members. CALM-LQTS and CALM-CPVT are the prevalent phenotypes. Primary neurological manifestations, unrelated to post-anoxic sequelae, manifested in 20 patients. Calmodulinopathy remains associated with a high arrhythmic event rate (symptomatic patients, n = 103, 74%). However, compared with the original 2019 cohort, there was a reduced frequency and severity of all cardiac events (61% vs. 85%; P = .001) and sudden death (9% vs. 27%; P = .008). Data on therapy do not allow definitive recommendations. Cardiac structural abnormalities, either cardiomyopathy or congenital heart defects, are present in 30% of patients, mainly CALM-LQTS, and lethal cases of heart failure have occurred. The number of familial cases and of families with strikingly different phenotypes is increasing.

CONCLUSION

Calmodulinopathy has pleiotropic presentations, from channelopathy to syndromic forms. Clinical severity ranges from the early onset of life-threatening arrhythmias to the absence of symptoms, and the percentage of milder and familial forms is increasing. There are no hard data to guide therapy, and current management includes pharmacological and surgical antiadrenergic interventions with sodium channel blockers often accompanied by an implantable cardioverter-defibrillator.

Meningitis caused by Chromobacterium haemolyticum suspected to be derived from a canal in Japan: a case report

BACKGROUND

The genus Chromobacterium, of which 12 species have been recognized, comprises bacteria that reside in tropical and subtropical environments. Of these species, Chromobacterium violaceum and Chromobacterium haemolyticum are known to cause infections in humans. There have been few reports of infections caused by Chromobacterium haemolyticum.

CASE PRESENTATION

Chromobacterium haemolyticum was detected in spinal fluid and blood samples isolated from a 73-year-old Japanese male patient who fell into a canal in Kyoto City, Japan and developed bacteremia and meningitis. Although meropenem and vancomycin were administered, this patient died 9 days after admission. Although the infection was misidentified as being caused by Chromobacterium violaceum by conventional identification methods, average nucleotide identity analysis revealed that the causative pathogen was Chromobacterium haemolyticum. The same bacteria were also detected in the canal in which the accident occurred. Phylogenetic analysis of the strain isolated from the patient and the strain isolated from the canal suggested that the two strains were very closely related.

CONCLUSIONS

Chromobacterium haemolyticum can be misidentified as Chromobacterium violaceum by conventional identification methods and tends to be more resistant to β-lactams than Chromobacterium violaceum. Pigment production and β-hemolysis on blood sheep agar can provide clues for the early identification of Chromobacterium haemolyticum.

Non-missense variants of KCNH2 show better outcomes in type 2 long QT syndrome

AIMS

More than one-third of type 2 long QT syndrome (LQT2) patients carry KCNH2 non-missense variants that can result in haploinsufficiency (HI), leading to mechanistic loss-of-function. However, their clinical phenotypes have not been fully investigated. The remaining two-thirds of patients harbour missense variants, and past studies uncovered that most of these variants cause trafficking deficiency, resulting in different functional changes: either HI or dominant-negative (DN) effects. In this study, we examined the impact of altered molecular mechanisms on clinical outcomes in LQT2 patients.

METHODS AND RESULTS

We included 429 LQT2 patients (234 probands) carrying a rare KCNH2 variant from our patient cohort undergoing genetic testing. Non-missense variants showed shorter corrected QT (QTc) and less arrhythmic events (AEs) than missense variants. We found that 40% of missense variants in this study were previously reported as HI or DN. Non-missense and HI-groups had similar phenotypes, while both exhibited shorter QTc and less AEs than the DN-group. Based on previous work, we predicted the functional change of the unreported variants-whether they cause HI or DN via altered functional domains-and stratified them as predicted HI (pHI)- or pDN-group. The pHI-group including non-missense variants exhibited milder phenotypes compared to the pDN-group. Multivariable Cox model showed that the functional change was an independent risk of AEs (P = 0.005).

CONCLUSION

Stratification based on molecular biological studies enables us to better predict clinical outcomes in the patients with LQT2.

Continuous Bayesian variant interpretation accounts for incomplete penetrance among Mendelian cardiac channelopathies

PURPOSE

The congenital Long QT Syndrome (LQTS) and Brugada Syndrome (BrS) are Mendelian autosomal dominant diseases that frequently precipitate fatal cardiac arrhythmias. Incomplete penetrance is a barrier to clinical management of heterozygotes harboring variants in the major implicated disease genes KCNQ1, KCNH2, and SCN5A. We apply and evaluate a Bayesian penetrance estimation strategy that accounts for this phenomenon.

METHODS

We generated Bayesian penetrance models for KCNQ1-LQT1 and SCN5A-LQT3 using variant-specific features and clinical data from the literature, international arrhythmia genetic centers, and population controls. We analyzed the distribution of posterior penetrance estimates across 4 genotype-phenotype relationships and compared continuous estimates with ClinVar annotations. Posterior estimates were mapped onto protein structure.

RESULTS

Bayesian penetrance estimates of KCNQ1-LQT1 and SCN5A-LQT3 are empirically equivalent to 10 and 5 clinically phenotype heterozygotes, respectively. Posterior penetrance estimates were bimodal for KCNQ1-LQT1 and KCNH2-LQT2, with a higher fraction of missense variants with high penetrance among KCNQ1 variants. There was a wide distribution of variant penetrance estimates among identical ClinVar categories. Structural mapping revealed heterogeneity among "hot spot" regions and featured high penetrance estimates for KCNQ1 variants in contact with calmodulin and the S6 domain.

CONCLUSIONS

Bayesian penetrance estimates provide a continuous framework for variant interpretation.

Novel Calmodulin Variant p.E46K Associated With Severe Catecholaminergic Polymorphic Ventricular Tachycardia Produces Robust Arrhythmogenicity in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

BACKGROUND

CaM (calmodulin) is a ubiquitously expressed, multifunctional Ca²⁺ sensor protein that regulates numerous proteins. Recently, CaM missense variants have been identified in patients with malignant inherited arrhythmias, such as long QT syndrome and catecholaminergic polymorphic ventricular tachycardia (CPVT). However, the exact mechanism of CaM-related CPVT in human cardiomyocytes remains unclear. In this study, we sought to investigate the arrhythmogenic mechanism of CPVT caused by a novel variant using human induced pluripotent stem cell (iPSC) models and biochemical assays.

METHODS

We generated iPSCs from a patient with CPVT bearing CALM2 p.E46K. As comparisons, we used 2 control lines including an isogenic line, and another iPSC line from a patient with long QT syndrome bearing CALM2 p.N98S (also reported in CPVT). Electrophysiological properties were investigated using iPSC-cardiomyocytes. We further examined the RyR2 (ryanodine receptor 2) and Ca²⁺ affinities of CaM using recombinant proteins.

RESULTS

We identified a novel de novo heterozygous variant, CALM2 p.E46K, in 2 unrelated patients with CPVT accompanied by neurodevelopmental disorders. The E46K-cardiomyocytes exhibited more frequent abnormal electrical excitations and Ca²⁺ waves than the other lines in association with increased Ca²⁺ leakage from the sarcoplasmic reticulum via RyR2. Furthermore, the [³H]ryanodine binding assay revealed that E46K-CaM facilitated RyR2 function especially by activating at low [Ca²⁺] levels. The real-time CaM-RyR2 binding analysis demonstrated that E46K-CaM had a 10-fold increased RyR2 binding affinity compared with wild-type CaM which may account for the dominant effect of the mutant CaM. Additionally, the E46K-CaM did not affect CaM-Ca²⁺ binding or L-type calcium channel function. Finally, antiarrhythmic agents, nadolol and flecainide, suppressed abnormal Ca²⁺ waves in E46K-cardiomyocytes.

CONCLUSIONS

We, for the first time, established a CaM-related CPVT iPSC-CM model which recapitulated severe arrhythmogenic features resulting from E46K-CaM dominantly binding and facilitating RyR2. In addition, the findings in iPSC-based drug testing will contribute to precision medicine.

Computerized misinterpretation of QT interval in 12‐lead electrocardiogram and its clinical consequences: A case of recurrent syncope

Don't blindly accept the automated assessment of electrocardiogram. It is important to raise long QT syndrome to the differential diagnosis of repeated syncope.

Disrupted CaV1.2 selectivity causes overlapping long QT and Brugada syndrome phenotypes in the CACNA1C-E1115K iPS cell model

BACKGROUND

A missense mutation in the α1c subunit of voltage-gated L-type Ca²⁺ channel-coding CACNA1C-E1115K, located in the Ca²⁺ selectivity site, causes a variety of arrhythmogenic phenotypes.

OBJECTIVE

We aimed to investigate the electrophysiological features and pathophysiological mechanisms of CACNA1C-E1115K in patient-specific induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CMs).

METHODS

We generated iPSCs from a patient carrying heterozygous CACNA1C-E1115K with overlapping phenotypes of long QT syndrome, Brugada syndrome, and mild cardiac dysfunction. Electrophysiological properties were investigated using iPSC-CMs. We used iPSCs from a healthy individual and an isogenic iPSC line corrected using CRISPR-Cas9-mediated gene editing as controls. A mathematical E1115K-CM model was developed using a human ventricular cell model.

RESULTS

Patch-clamp analysis revealed that E1115K-iPSC-CMs exhibited reduced peak Ca²⁺ current density and impaired Ca²⁺ selectivity with an increased permeability to monovalent cations. Consequently, E1115K-iPSC-CMs showed decreased action potential plateau amplitude, longer action potential duration (APD), and a higher frequency of early afterdepolarization compared with controls. In optical recordings examining the antiarrhythmic drug effect, late Na⁺ channel current (I_NaL) inhibitors (mexiletine and GS-458967) shortened APDs specifically in E1115K-iPSC-CMs. The AP-clamp using a voltage command obtained from E1115K-iPSC-CMs with lower action potential plateau amplitude and longer APD confirmed the upregulation of I_NaL. An in silico study recapitulated the in vitro electrophysiological properties.

CONCLUSION

Our iPSC-based analysis in CACNA1C-E1115K with disrupted Ca_V1.2 selectivity demonstrated that the aberrant currents through the mutant channels carried by monovalent cations resulted in specific action potential changes, which increased endogenous I_NaL, thereby synergistically contributing to the arrhythmogenic phenotype.

Targeted deep sequencing analyses of long QT syndrome in a Japanese population

Long QT syndrome (LQTS) is one of the most common inherited arrhythmias and multiple genes have been reported as causative. Presently, genetic diagnosis for LQTS patients is becoming widespread and contributing to implementation of therapies. However, causative genetic mutations cannot be detected in about 20% of patients. To elucidate additional genetic mutations in LQTS, we performed deep-sequencing of previously reported 15 causative and 85 candidate genes for this disorder in 556 Japanese LQTS patients. We performed in-silico filtering of the sequencing data and found 48 novel variants in 33 genes of 53 cases. These variants were predicted to be damaging to coding proteins or to alter the binding affinity of several transcription factors. Notably, we found that most of the LQTS-related variants in the RYR2 gene were in the large cytoplasmic domain of the N-terminus side. They might be useful for screening of LQTS patients who had no known genetic factors. In addition, when the mechanisms of these variants in the development of LQTS are revealed, it will be useful for early diagnosis, risk stratification, and selection of treatment.

Case Report of a Ventricular Fibrillation Storm with a Cardiac Conduction Disorder and HCN4 Variant 18 Years after Ablation of Atrial Flutter

Background

Genetic abnormalities causing various arrhythmias including atrial arrhythmias, specialized cardiac conduction disorders, and malignant ventricular arrhythmias have been reported. However, it is sometimes difficult to diagnose and treat patients with various arrhythmias.

Case summary

A 49-year-old woman who underwent ablation of typical atrial flutter (AFL) at 31 years of age visited the emergency room due to a cardiopulmonary arrest. Her 12-lead electrocardiogram during sinus rhythm after resuscitation exhibited first-degree atrioventricular block with right bundle branch block and right axis deviation. No structural heart disease was evident on standard imaging screening. An implantation of a single-chamber implantable cardioverter defibrillator (ICD) was indicated. After the ICD implantation, she then experienced multiple ventricular fibrillation (VF) episodes. Radiofrequency catheter ablation of triggered ventricular premature contractions (VPCs) was performed but failed because the clinical VPCs could not be induced during the session. Although no pathogenic variants associated with Brugada syndrome or long-QT syndrome were found, a rare HCN4 variant, c.1209+2_1209+3insGAGT (rs786205418), was identified in a gene panel analysis. Because high-frequency clinical pacing was effective for suppressing the VF, the single-chamber ICD was upgraded to a dual-chamber ICD. Thereafter, high-rate pacing successfully prevented any further ventricular arrhythmias during the follow up.

Discussion

A clinical course with prominent wide QRS complexes and AFL in one’s early 30s followed by sudden onset of a VF storm about 20 years later is extremely rare. Her clinical phenotype expression was possibly associated with a rare HCN4 variant; however, further study is needed to confirm whether this variant was pathological or not.

Improvement in Decline Rate of Estimated Glomerular Filtration Rate after Febuxostat Treatment in a Fabry Disease Patient with Enzyme Replacement Therapy-resistant Proteinuria

Fabry disease is an inherited lysosomal disorder caused by mutations in the alpha-galactosidase A gene. We herein report a Fabry disease patient with enzyme replacement therapy (ERT)-resistant proteinuria who showed improvement in the estimated glomerular filtration rate (eGFR) decline rate after uric acid (UA)-lowering therapy. The patient was diagnosed with Fabry disease at 36 years old. After that, even under ERT, proteinuria and eGFR decline persisted. During the clinical course, serum UA levels were elevated with increases in renal tubular damage markers. Febuxostat administration immediately improved tubular damage and prevented further eGFR decline. UA-mediated tubulopathy may become an additional therapeutic target for eGFR decline in Fabry disease.

Desmoglein 2 mutant mice reproduce arrhythmogenic right ventricular cardiomyopathy patients' phenotype

Background

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) is inherited cardiac disease with unresolved treatment. ARVC is progressive and leads to lethal arrhythmias and terminal heart failure. Most often encountered ARVC mutations are in desmosomal genes [1].

Purpose

We aimed to generate transgenic mice with exact copy of genetic defects found in Japanese cohort of ARVC patients, describe the phenotype, and identify target for curative therapy.

Methods

CRISPR/Cas9 genome editing was used to generate knock-in mice with the two most common point mutations in Japanese ARVC patients: DSG2 292R&gt;C and 494D&gt;A [2] (mouse equivalent positions are 297R and 499D, respectively). To analyze the phenotype of mice we used imaging techniques - cardiac echography and MRI as well as telemetry, treadmill, immunohistochemistry, confocal microscopy, histology, Western blot.

Results

In vivo observations of transgenic mice demonstrated inequalities in phenotypical presentation between the two mutations. Some of 297C mice (both hetero- and homozygous) died suddenly, starting from the age of 9 weeks, in contrast to surviving all 499A carriers. Dissection of suddenly died mice reveals enlarged cardiac cavities, mainly in the right heart. In addition, 297C homozygous hearts present with pale zones scattered all over the heart. Paraffin sections from this hearts stained with hematoxilin/eosin and Masson's trichrome show myocardial areas with absent myocytes, collagen accumulation and calcifications. With exception of homozygous 297C mice, spontaneous development of cardiac phenotype in Dsg2 knock-in mice starts after 25th weeks of age. Both mutant mice gradually developed cardiac dysfunction (echography and MRI, Fig. 1) and echographically visible left ventricular wall infiltrations. Heterozygous 297C mutation produces more severe phenotype that develops earlier. Similar to human ARVC, the degree of cardiac damage vary significantly. It is known from the human ARVC that physical activity aggravates the ARVC phenotype and may cause sudden cardiac death. To evaluate the effect of physical stress on the phenotype of Dsg2 knock-in mice we subjected 11 weeks old animals on treadmill exercise. Training for 8 weeks provoked development of heart failure in both 297C and 499A mutant mice, significantly earlier than natural progress of the phenotype. No mouse died suddenly. Telemetry experiment demonstrated electrical instability in 297C homozygous hearts showing conduction and rhythm abnormalities (Fig. 2). Apoptosis was detected in both mutant mice by TUNEL staining and confocal microscopy. Dsg2 protein expression was not affected by the mutations.

Conclusion

We generated mouse model of ARVC that reproduces exact genetic defect of the human disease. There are significant similarities between our model and ARVC patients' phenotype.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Japanese KAKENHI funding

Calmodulinopathy is a common cause of critical cardiac phenotypes in fetus and infancy

Background

Cardiac calmodulinopathy is a life-threatening arrhythmia syndrome which presents several phenotypes of inherited primary arrhythmia syndrome (IPAS), and caused by mutations in calmodulin-encoded genes (CALM1–3). We aimed clarify the frequency and their clinical characteristics of calmodulinopathy in our IPAS cohort.

Methods

By using next generation sequencing, we screened arrhythmia related genes including calmodulin-encoding genes in 322 unrelated symptomatic children (0–12 years) who were suspected as IPAS; they included 40 cases with lethal arrhythmic attacks (LAE) under 6-year-old. After gene screening, we investigated their physiological and clinical characteristics about mutation carriers.

Results

Among 322 children, we identified 6 mutations of calmodulin-encoded genes in 9 probands (2.8%); one CALM1 in 2 probands (N98S), and 5 CALM2 in 7 probands (E46K, D96V, D96G, N98S, E141K). Their clinical diagnoses were long QT syndrome (LQTS, n=4), catecholaminergic polymorphic ventricular tachycardia (CPVT, n=3) and both (n=2). Their age of diagnosis ranges at 0–9 with the median of 5 years. There were three major clinical phenotypes; 1) CALM2-D96V, and E141K: two infants with advanced atrio-ventricular block, significant QTc prolongation, severe heart failure from their fetal period – both of them deceased within 1.5-year-old. Their clinical phenotypes resembled classical Timothy syndrome caused by CACNA1C mutations. 2) CALM1-N98S (n=2), CALM2-N98S (n=2), and CALM2-D96G: four preschoolers with LAEs and one syncope: all of them were 3–5 years old. In addition, a T wave morphology of CALM2-D96G carrier was very similar to LQT1. 3) CALM2-E46K (n=2): two were first diagnosed with neurological and developmental disorders, and showed phenotype of CPVT: their cardiac phenotypes were milder compared with that of 1) or 2). Overall, these phenotypes seemed to be mutation specific (indicated in figure). Their cardiac features were severer, and the onset of LAEs was earlier compared with other genotypes of LQTS/CPVT. As the treatment, β-blocker was effective for control of LAEs.

Conclusion

Cardiac calmodulinopathy presented serious and potentially lethal phenotypes in fetus or infancy. To prevent cardiac death in them, we must correctly diagnose and start the treatment as earlier as possible.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): MEXT KAKENHI from the Ministry of Education, Culture, Sports, Science, and Technology of Japan

Different prognosis of ARVC patients between DSG2 and PKP2 variant carriers

Background

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiomyopathy mainly caused by desmosomal gene variants. In Europe and North America, pathogenic variants in PKP2 were identified in most of the ARVC patients. On the other hand, we have reported that the genetic backgrounds of ARVC in Japanese were different from those in European; pathogenic variants in DSG2 were predominant in Japanese. Genotype-phenotype correlations, however, have not been clarified yet.

Purpose

In this study, we aimed to examine whether the genotype affect the phenotype and outcome in Japanese ARVC patients.

Methods and results

This study included 167 Japanese ARVC patients who received genetic testing (128 males [77%]). Their median age at diagnosis was 44 [24–55] years old and median follow-up duration was 10 [4–21] years. We found 90 patients with pathogenic variants: 52 in DSG2 (31%), 30 in PKP2 (18%), 3 in DSP (1.8%), 1 in DSC (0.6%), 1 in JUP (0.6%) and 3 in DES (1.8%). The age of the first sustained ventricular arrhythmia (SVT) were older in the patients with DSG2 than those with PKP2 variants (48±15 years vs. 35±15 years, P=0.008) but younger in DSG2 variant carriers at the first hospitalization for heart failure (41 [22–61] years vs. 67 [61–74] years, P=0.03). The left ventricular ejection fractions of DSG2 variant carriers were significantly lower at diagnosis than that of PKP2 (52 [41–60] % vs. 61 [56–66] %, P=0.002). Kaplan-Meier survival curve for lethal arrhythmic events including SVT, ventricular fibrillation and sudden death revealed that the event rate of DSG2 variant carriers was significantly lower than that of PKP2 (log-rank test, P=0.02) (Fig. 1).

Among 11 patients who had both SVT and hospitalizations for HF, 7 PKP2 variant carriers had SVT first, then, hospitalized for HF (48 [35–53] years and 67 [55–71] years, P=0.02). Contrary, the clinical course of 4 DSG2 variants carriers were different from those with PKP2 (54 [40–68] years for SVT and 65 [56–70, P=0.1] years for HF) (Fig. 2).

Conclusion

The patients with DSG2, which is the major causative gene for ARVC in Japanese, show different phenotype and outcome from those with PKP2. We should examine the effect of variants on the prognosis of ARVC patients in more large population including various ethnics.

Funding Acknowledgement

Type of funding sources: None.

Arrhythmogenic right ventricular cardiomyopathy with plakophilin-2 genetic variant concomitant with early manifestation of ventricular tachyarrhythmia: A case series

Background

Arrhythmogenic right-ventricular cardiomyopathy (ARVC) is a hereditary cardiomyopathy characterized by fibro-fat replacement of the right-ventricular myocardium. There are many factors associated with poor prognosis in patients with ARVC. Among these factors, intensive physical exertion is considered an important risk factor for sudden cardiac death.

Case summary

Herein, we report a case series of siblings with ARVC and an early manifestation of ventricular tachyarrhythmia. Plakophilin-2 (PKP2) genetic variant, which is one of the causative genetic variants of ARVC, was detected by genetic testing in all three siblings. They were young athletes with lethal/symptomatic ventricular tachycardias. The eldest sibling was implanted with a transvenous implantable cardioverter defibrillator (ICD) due to resuscitated cardiopulmonary arrest at 18 years of age; the next oldest patient was treated with successful catheter ablation at 17 years; the youngest patient was treated with catheter ablation and subcutaneous ICD implantation at 17 years.

Discussion

A recent experimental model revealed that physical exertion in PKP2 knockout mice diminished cardiac muscle mass and increased cardiac myocyte apoptosis, despite enhanced arrhythmogenicity such as increased fractional shortening and calcium transient amplitude. The three siblings were heterozygous for the previously reported pathologic splice site variant c.2489 + 1G > A in Intron 12 of the PKP2. The variant might play an important role in facilitating the vulnerability to arrhythmia under intensive endurance training. Most ARVC patients with PKP2 variant, especially pathologic splice site variant c.2489 + 1G > A in Intron 12 of the PKP2, might have to be managed strictly regarding daily exercise.

Cytosolic Ca2+-dependent Ca2+ release activity primarily determines the ER Ca2+ level in cells expressing the CPVT-linked mutant RYR2

Type 2 ryanodine receptor (RYR2) is a cardiac Ca2+ release channel in the ER. Mutations in RYR2 are linked to catecholaminergic polymorphic ventricular tachycardia (CPVT). CPVT is associated with enhanced spontaneous Ca2+ release, which tends to occur when [Ca2+]ER reaches a threshold. Mutations lower the threshold [Ca2+]ER by increasing luminal Ca2+ sensitivity or enhancing cytosolic [Ca2+] ([Ca2+]cyt)-dependent activity. Here, to establish the mechanism relating the change in [Ca2+]cyt-dependent activity of RYR2 and the threshold [Ca2+]ER, we carried out cell-based experiments and in silico simulations. We expressed WT and CPVT-linked mutant RYR2s in HEK293 cells and measured [Ca2+]cyt and [Ca2+]ER using fluorescent Ca2+ indicators. CPVT RYR2 cells showed higher oscillation frequency and lower threshold [Ca2+]ER than WT cells. The [Ca2+]cyt-dependent activity at resting [Ca2+]cyt, Arest, was greater in CPVT mutants than in WT, and we found an inverse correlation between threshold [Ca2+]ER and Arest. In addition, lowering RYR2 expression increased the threshold [Ca2+]ER and a product of Arest, and the relative expression level for each mutant correlated with threshold [Ca2+]ER, suggesting that the threshold [Ca2+]ER depends on the net Ca2+ release rate via RYR2. Modeling reproduced Ca2+ oscillations with [Ca2+]cyt and [Ca2+]ER changes in WT and CPVT cells. Interestingly, the [Ca2+]cyt-dependent activity of specific mutations correlated with the age of disease onset in patients carrying them. Our data suggest that the reduction in threshold [Ca2+]ER for spontaneous Ca2+ release by CPVT mutation is explained by enhanced [Ca2+]cyt-dependent activity without requiring modulation of the [Ca2+]ER sensitivity of RYR2.

Successful Management of a Young Athlete with Type 2 Long QT Syndrome by Genotype-specific Risk Stratification and Bridging Therapy with a Wearable Cardioverter Defibrillator

We herein report a 14-year-old boy with repetitive nocturnal syncope related to medication-refractory long QT syndrome (LQTS). Although the use of an implantable cardioverter-defibrillator (ICD) was inevitable to prevent sudden cardiac death, he refused immediate implantation in order to play in a baseball competition six weeks away. Given his genetic diagnosis of type 2 LQTS, which is associated with cardiac events unrelated to exercise, we prescribed a wearable cardioverter defibrillator (WCD) to be donned at night, without limiting his exercise participation. An ICD was implanted after the competition. We successfully performed the preplanned treatment while maximizing the patient's quality-of-life with a WCD and genotype-specific risk stratification.

Oral Adrenergic Agents Produced Ventricular Fibrillation and QT Prolongation in an Elderly Patient Carrying an RYR2 Variant

Mutant cardiac ryanodine receptor channels (RyR2) are "leaky," and spontaneous Ca²⁺ release through these channels causes delayed afterdepolarizations that can deteriorate into ventricular fibrillation. Some patients carrying RYR2 mutations in type 1 catecholaminergic polymorphic ventricular tachycardia exhibit QT prolongation and are initially diagnosed with long QT syndrome. However, none have been reported to cause drug-induced ventricular fibrillation in patients with RYR2 variants. We describe the first case of an elderly woman with drug-induced QT prolongation and ventricular fibrillation who carried a novel RYR2 variant but no other mutations related to long QT syndrome. Oral adrenergic agents might induce QT prolongation and subsequent ventricular fibrillation in patients carrying an RYR2 variant. Screening for RYR2 could be valuable in patients with suspected drug-induced long QT syndrome.

Association Between Deleterious SCN5A Variants and Ventricular Septal Defect in Young Patients With Brugada Syndrome

OBJECTIVES

This study aimed to investigate the clinical characteristics of young patients with Brugada syndrome (BrS) with ventricular septal defect (VSD) and explore their genetic backgrounds.

BACKGROUND

VSD is the most frequently occurring congenital heart disease among children. In contrast, BrS is a rare hereditary disease that is responsible for ventricular fibrillation and sudden cardiac death. Owing to their low incidence, the genetic background and clinical characteristics of patients with BrS with VSD have not been elucidated yet.

METHODS

This study enrolled 36 individuals who were diagnosed with BrS when they were <20 years of age and performed genetic screening for SCN5A. The functional alteration in mutant Na⁺ channels was confirmed by patch clamp technique.

RESULTS

Among the 36 patients with BrS, 5 had been diagnosed with VSD. This study found 14 heterozygous SCN5A variants in 15 unrelated patients. The 5 patients with VSD carried SCN5A variants, including R367S, R535∗, R893C, W1345C, and G1743R. The 3 missense variants (R893C, W1345C, and G1743R) have been proved to reduce peak Na⁺ current to <10%. A functional analysis of SCN5A R367S was performed and the variant was found to be nonfunctional.

CONCLUSIONS

This study identified 5 loss-of-function SCN5A variants in 5 young patients with BrS with VSD. The study hypothesizes that altered blood flow in the right ventricular outflow tract leads to fibrosis and electrophysiological changes, predisposing the patients to earlier clinical presentation of BrS. In patients with VSD and ST-segment elevation in the right precordial leads, BrS should be considered and appropriate screening should be pursued accordingly.

Impact of cascade screening for catecholaminergic polymorphic ventricular tachycardia type 1

Objective

Human cardiac ryanodine receptor 2 (RYR2) shows autosomal-dominant inheritance in catecholaminergic polymorphic ventricular tachycardia type 1 (CPVT1); however, de novo variants have been observed in sporadic cases. Here, we investigated CPVT1-related RYR2 variant inheritance and its clinical significance between familial and de novo cases.

Methods

We enrolled 82 independent CPVT1 probands (median age: 10.0 (7.0–13.0) years; 45 male) carrying the RYR2 variants and whose biological origin could be confirmed by parental genetic analysis: assured familial inheritance (familial group: n=24) and de novo variants (de novo group: n=58). We examined the clinical characteristics of the probands and their family members carrying the RYR2 variants.

Results

In the de novo group, the RYR2 variants were more likely located in the C-terminus domain and less likely in the N-terminus domain than those in the familial group. The cumulative incidence of the first cardiac events (syncope and cardiac arrest (CA) or CA only) of the probands at the age of 5 and 10 years was higher in the de novo group than in the familial group. Nearly half of the probands in both groups experienced CA events before diagnosis. Only 37.5% of their genotype-positive parents had symptoms; however, at least 66.7% of the genotype-positive siblings were symptomatic.

Conclusions

CPVT1 probands harbouring de novo RYR2 variants showed an earlier onset of symptoms than those with assured familial inheritance. Cascade screening may enable early diagnosis, risk stratification and prophylactic therapeutic intervention to prevent sudden cardiac death of probands and potential genotype-positive family members.

School-based routine screenings of electrocardiograms for the diagnosis of long QT syndrome

Aims

School-based routine screenings of electrocardiograms (ECGs) have been performed upon admission to primary school (PS), junior high school (JHS), and high school (HS) in Japan. Though ECGs with prolonged QT intervals are occasionally found, the role of regular ECG screening tests in identifying long QT syndrome (LQTS) remains to be determined. We investigated the usefulness of the ECG screenings by comparing the results of genetic tests between students who showed QT-prolongation in the screenings and patients with LQTS.

Methods and results

We genetically screened 341 students (106 PS, 173 JHS, and 62 HS). Of these, 230 subjects showed QT-prolongation during regular screenings (S-S group), and the other 111 patients were clinically consulted with suspected LQTS by paediatricians (C-C group). Genotype–phenotype relationships were compared between the two groups. The positive rates in the genetic tests were comparable among the two groups; however, symptomatic subjects were significantly fewer in the S-S group than the C-C group (3% vs. 70%). Compared to the genotype-negative subjects, the positive subjects showed significantly longer QTc (P &lt; 0.0001) and more frequently presented LQTS risk scores with ≥3.5 points (P &lt; 0.0001). Lethal arrhythmic events (LAE) occurred only in the C-C group; 18 subjects experienced LAE and 83% of them were found to carry variant(s) in the LQTS-related genes.

Conclusion

The school-based ECG screenings are effective in identifying young patients with LQTS who require genetic analysis. If individuals are screened at a younger age, we can identify patients at risk earlier and provide preventative treatments.

An International Multi-Center Cohort Study on β-blockers for the Treatment of Symptomatic Children with Catecholaminergic Polymorphic Ventricular Tachycardia

Background: Symptomatic children with catecholaminergic polymorphic ventricular tachycardia (CPVT) are at risk for recurrent arrhythmic events. Beta-blockers (BBs) decrease this risk, but studies comparing individual BBs in sizeable cohorts are lacking. We aimed to assess the association between risk for arrhythmic events and type of BB in a large cohort of symptomatic children with CPVT. Methods: From two international registries of patients with CPVT, RYR2 variant-carrying symptomatic children (defined as syncope or sudden cardiac arrest prior to BB initiation and age at start of BB therapy <18 years), treated with a BB were included. Cox-regression analyses with time-dependent covariates for BB and potential confounders were used to assess the hazard ratio (HR). The primary outcome was the first occurrence of sudden cardiac death, sudden cardiac arrest, appropriate implantable cardioverter-defibrillator shock, or syncope. The secondary outcome was the first occurrence of any of the primary outcomes except syncope. Results: We included 329 patients (median age at diagnosis 12 [interquartile range, 7-15] years, 35% females). Ninety-nine (30.1%) patients experienced the primary and 74 (22.5%) experienced the secondary outcome during a median follow-up of 6.7 [interquartile range, 2.8-12.5] years. Two-hundred sixteen patients (66.0%) used a non-selective BB (predominantly nadolol [n=140] or propranolol [n=70]) and 111 (33.7%) used a β1-selective BB (predominantly atenolol [n=51], metoprolol [n=33], or bisoprolol [n=19]) as initial BB. Baseline characteristics did not differ. The HR for both the primary and secondary outcomes were higher for β1-selective compared with non-selective BBs (HR, 2.04 95% CI, 1.31-3.17; and HR, 1.99; 95% CI, 1.20-3.30, respectively). When assessed separately, the HR for the primary outcome was higher for atenolol (HR, 2.68; 95% CI, 1.44-4.99), bisoprolol (HR, 3.24; 95% CI, 1.47-7.18), and metoprolol (HR, 2.18; 95% CI, 1.08-4.40) compared with nadolol, but did not differ from propranolol. The HR of the secondary outcome was only higher in atenolol compared with nadolol (HR, 2.68; 95% CI, 1.30-5.55). Conclusions: B1-selective BBs were associated with a significantly higher risk for arrhythmic events in symptomatic children with CPVT compared with non-selective BBs, specifically nadolol. Nadolol, or propranolol if nadolol is unavailable, should be the preferred BB for treating symptomatic children with CPVT.

Sudden death after inappropriate shocks of implantable cardioverter defibrillator in a catecholaminergic polymorphic ventricular tachycardia case with a novel RyR2 mutation

BACKGROUND

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmogenic syndrome and a cause of exercise-related sudden death. CPVT has been reported to be caused by gain of function underlying a mutation of cardiac ryanodine receptor (RyR2).

METHODS

In a family with a CPVT patient, genomic DNA was extracted from peripheral blood lymphocytes, and the RyR2 gene underwent target gene sequence using MiSeq. The activity of wild-type (WT) and mutant RyR2 channel were evaluated by monitoring Ca²⁺ signals in HEK293 cells expressing WT and mutant RyR2. We investigated a role of a RyR2 mutation in the recent tertiary structure of RyR2.

RESULTS

Though a 17-year-old man diagnosed as CPVT had implantable cardioverter defibrillator (ICD) and was going to undergo catheter ablation for the control of paroxysmal atrial fibrillation, he suddenly died at the age of twenty-one because of ventricular fibrillation which was spontaneously developed after maximum inappropriate ICD shocks against rapid atrial fibrillation. The genetic test revealed a de novo RyR2 mutation, Gln4936Lys in mosaicism which was located at the α-helix interface between U-motif and C-terminal domain. In the functional analysis, Ca²⁺ release from endoplasmic reticulum via the mutant RyR2 significantly increased than that from WT.

CONCLUSION

A RyR2 mutation, Gln4936Lys, to be documented in a CPVT patient with exercise-induced ventricular tachycardias causes an excessive Ca²⁺ release from the sarcoplasmic reticulum which corresponded to clinical phenotypes of CPVT. The reduction of inappropriate shocks of ICD is essential to prevent unexpected sudden death in patients with CPVT.

Loss-of-function mutations in cardiac ryanodine receptor channel cause various types of arrhythmias including long QT syndrome

AIMS

Gain-of-function mutations in RYR2, encoding the cardiac ryanodine receptor channel (RyR2), cause catecholaminergic polymorphic ventricular tachycardia (CPVT). Whereas, genotype-phenotype correlations of loss-of-function mutations remains unknown, due to a small number of analysed mutations. In this study, we aimed to investigate their genotype-phenotype correlations in patients with loss-of-function RYR2 mutations.

METHODS AND RESULTS

We performed targeted gene sequencing for 710 probands younger than 16-year-old with inherited primary arrhythmia syndromes (IPAS). RYR2 mutations were identified in 63 probands, and 3 probands displayed clinical features different from CPVT. A proband with p.E4146D developed ventricular fibrillation (VF) and QT prolongation whereas that with p.S4168P showed QT prolongation and bradycardia. Another proband with p.S4938F showed short-coupled variant of torsade de pointes (scTdP). To evaluate the functional alterations in these three mutant RyR2s and p.K4594Q previously reported in a long QT syndrome (LQTS), we measured Ca2+ signals in HEK293 cells and HL-1 cardiomyocytes as well as Ca2+-dependent [3H]ryanodine binding. All mutant RyR2s demonstrated a reduced Ca2+ release, an increased endoplasmic reticulum Ca2+, and a reduced [3H]ryanodine binding, indicating loss-of-functions. In HL-1 cells, the exogenous expression of S4168P and K4594Q reduced amplitude of Ca2+ transients without inducing Ca2+ waves, whereas that of E4146D and S4938F evoked frequent localized Ca2+ waves.

CONCLUSION

Loss-of-function RYR2 mutations may be implicated in various types of arrhythmias including LQTS, VF, and scTdP, depending on alteration of the channel activity. Search of RYR2 mutations in IPAS patients clinically different from CPVT will be a useful strategy to effectively discover loss-of-function RYR2 mutations.

Early onset of heart failure in Japanese ARVC patients with pathogenic desmosomal gene variants

Background

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiomyopathy mainly caused by desmosomal gene variants. Although there are a lot of reports regarding to European ARVC patients, the ones in Asian are a few, and the characteristics of Asian ARVC have been still unclear. We have reported that the genetic backgrounds in Japanese ARVC patients were different from those in European ones. In this study, we aimed to examine the phenotype and outcome of Japanese ARVC patients with specific genetic backgrounds.

Methods and results

This study included 104 Japanese ARVC patients who were diagnosed as definite in the 2010 Task Force Criteria for ARVC and received genetic analysis (79 males [76%]; median age at diagnosis, 40 years [IQR 22–53 years].) Fifty-seven patients carried variants in desmosomal genes classified as pathogenic based on ACMG guideline: 30 in DSG2 (29%), 22 in PKP2 (21%), 2 in DSC2 (2%) and 3 in DSP (3%). The median age of diagnosis was significantly younger in the patients with the pathogenic variants than in those without (37 years [IQR 21–49 years] vs. 46 years [IQR 34–58 years], P=0.01). During a median follow-up of 9.3 years (IQR 3.5–20.9 years), 10 patients died and 2 were received heart transplantation. Sixty-two suffered lethal arrhythmic events including cardiopulmonary arrest, ventricular fibrillation, sustained ventricular tachycardia and appropriate shocks by implantable cardioverter defibrillator. Twenty-two were hospitalized for heart failure. There was no difference in these events rate between the two groups. However, survival analysis revealed that patients with pathogenic variants hospitalized for heart failure significantly earlier in their life than those without (P=0.04, log-rank test, Figure 1).

Conclusions

The Japanese ARVC patients with pathogenic variants in desmosomal genes are diagnosed and hospitalize for heart failure at younger age than those without. These findings have not been reported in other ethnics. Our study warns that we should be cautious for not only the prevention of lethal arrhythmic events but also the progress of the heart failure in Japanese ARVC patients with pathogenic variants.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Japan Agency for Medical Research and Development Figure 1

Electrocardiographic Diagnosis of Hypertrophic Cardiomyopathy in the Pre- and Post-Diagnostic Phases in Children and Adolescents

BACKGROUND

The usefulness of electrocardiographic (ECG) voltage criteria for diagnosing hypertrophic cardiomyopathy (HCM) in pediatric patients is poorly defined.Methods and Results:ECGs at the 1st grade (mean [±SD] age 6.6±0.3 years) were available for 11 patients diagnosed with HCM at around the 7th grade (13.2±0.3 years). ECGs were available for another 64 patients diagnosed with HCM in the 1st (n=15), 7th (n=32), and 10th (n=17) grades. Fifty-one voltage criteria were developed by grade and sex using 62,841 ECGs from the general population. Voltage criteria were set at the 99.95th percentile (1/2,000) point based on the estimated prevalence of childhood HCM (2.9 per 100,000 [1/34,483]) to decrease false negatives. Conventional criteria were from guidelines for school-aged children in Japan. Of 11 patients before diagnosis, 2 satisfied conventional criteria in 1st grade; 5 (56%) of the remaining 9 patients fulfilled 2 voltage criteria (R wave in limb-lead I [RI]+S wave in lead V3 [SV3] and R wave in lead V3 [RV3]+SV3). Robustness analysis for sensitivity showed RV3+SV3 was superior to RI+SV3. For all patients after diagnosis, RI+SV4 was the main candidate. However, conventional criteria were more useful than voltage criteria.

CONCLUSIONS

Early HCM prediction was possible using RV3+SV3 in >50% of patients in 1st grade. Voltage criteria may help diagnose prediagnostic or early HCM, and prevent tragic accidents, although further prospective studies are required.

Prevalence and characteristics of the Brugada electrocardiogram pattern in patients with arrhythmogenic right ventricular cardiomyopathy

BACKGROUND

Despite distinct pathophysiology, arrhythmogenic right ventricular cardiomyopathy (ARVC) and Brugada syndrome (BrS) exhibit overlapping phenotypes. We investigated the prevalence and characteristics of the Brugada electrocardiogram (ECG) pattern in ARVC patients.

METHODS

A total of 114 ARVC patients fulfilling the revised Task Force Criteria were enrolled. The Brugada ECG pattern was evaluated according to the consensus report on right precordial leads, and 1141 ECGs (median, 1; interquartile range, 1-16 ECGs/patient) were analyzed.

RESULTS

Five patients (4%) showed a Brugada ECG pattern, which disappeared in four patients with ECGs recorded more than 2 years afterward. ARVC patients with the Brugada ECG pattern had a longer PQ interval (220 ± 62 ms vs 180 ± 35 ms, P = .02) and longer QRS duration (138 ± 25 ms vs 102 ± 23 ms, P < .001) than patients without the pattern. During follow-up (median, 11.4; interquartile range, 5.5-17.1 years), 19 ARVC patients experienced cardiac death and 29 experienced heart failure (HF) hospitalization. Kaplan-Meier analysis determined that the Brugada ECG pattern increased the risk of cardiac death and HF hospitalization (log-rank; P < .001, P < .001 respectively). The mean J-point and S-wave amplitudes of the Brugada ECG pattern were 0.29 ± 0.05 mV and 0.34 ± 0.21 mV, respectively, which were significantly lower than those of 26 age-matched BrS patients with a previous ventricular fibrillation episode (0.66 ± 0.33 mV, P < .001 and 0.67 ± 0.39 mV, P = .02 respectively).

CONCLUSION

The Brugada ECG pattern was infrequently encountered, was transient in ARVC patients, and was associated with a longer PQ interval, longer QRS duration, and cardiac events.

Functionally validated SCN5A variants allow interpretation of pathogenicity and prediction of lethal events in Brugada syndrome

AIMS

The prognostic value of genetic variants for predicting lethal arrhythmic events (LAEs) in Brugada syndrome (BrS) remains controversial. We investigated whether the functional curation of SCN5A variations improves prognostic predictability.

METHODS AND RESULTS

Using a heterologous expression system and whole-cell patch clamping, we functionally characterized 22 variants of unknown significance (VUSs) among 55 SCN5A mutations previously curated using in silico prediction algorithms in the Japanese BrS registry (n = 415). According to the loss-of-function (LOF) properties, SCN5A mutation carriers (n = 60) were divided into two groups: LOF-SCN5A mutations and non-LOF SCN5A variations. Functionally proven LOF-SCN5A mutation carriers (n = 45) showed significantly severer electrocardiographic conduction abnormalities and worse prognosis associated with earlier manifestations of LAEs (7.9%/year) than in silico algorithm-predicted SCN5A carriers (5.1%/year) or all BrS probands (2.5%/year). Notably, non-LOF SCN5A variation carriers (n = 15) exhibited no LAEs during the follow-up period. Multivariate analysis demonstrated that only LOF-SCN5A mutations and a history of aborted cardiac arrest were significant predictors of LAEs. Gene-based association studies using whole-exome sequencing data on another independent SCN5A mutation-negative BrS cohort (n = 288) showed no significant enrichment of rare variants in 16 985 genes including 22 non-SCN5A BrS-associated genes as compared with controls (n = 372). Furthermore, rare variations of non-SCN5A BrS-associated genes did not affect LAE-free survival curves.

CONCLUSION

In vitro functional validation is key to classifying the pathogenicity of SCN5A VUSs and for risk stratification of genetic predictors of LAEs. Functionally proven LOF-SCN5A mutations are genetic burdens of sudden death in BrS, but evidence for other BrS-associated genes is elusive.

Pueraria mirifica, an estrogenic tropical herb, unveiled the severity of Type 1 LQTS caused by KCNQ1-T587M

After taking an estrogen-containing supplement derived from a tropical plant Pueraria mirifica, a 24-year-old woman presented marked QT prolongation and repetitive torsade de pointes. The patient was found to carry a heterozygous KCNQ1-T587M mutation. This is the first report on Pueraria mirifica-related acquired long QT syndrome.